Posted
by
kdawson
on Sunday January 18, 2009 @02:25PM
from the geo-exchange dept.

suraj.sun recommends a CNet post giving details of a still little-known energy technology: the ground source heat pump or geo-exchange system. This is distinct from so-called geothermal energy, which taps the heat in the earth to provide energy. Geo-exchange is suitable in scale for small industry — the article describes one commercial re-development of an old mill into apartment and commercial space that put in a geo-exchange at about half the cost of traditional fossil fuel-based alternatives. Even some individual homeowners are opting for this green method of heating and cooling, at a premium in price of about 50 percent (but costs are very much per-project, largely because drilling is involved). "Rather than use underground heat, geothermal heat pumps attached to buildings capitalize on the steady temperature of the ground or deep water wells. In effect, they treat the Earth like a giant energy savings bank, depositing or withdrawing heat depending on the time of year. "

Be warned - this won't work well in all kinds of ground. We've had such a heating system installed in our 200mÂ house about 20 years ago (Germany, with our oil prices we had to get creative a bit earlier than ppl in the US) and we had a lot of trouble with freezing probes (the things that go into the groud) because in the karst (ground with lots of lime in it and thus lots of small caves) they wouldn't keep proper contact with the earth.

Live in upstate NY - turned on our ground-source closed-loop heat pump end of November 2008. So far, so good.Last year when we bought the system nobody was talking about DX (and in this neck of the woods, they're still not.)

Couple of things I would speculate about with respect to DX:1 - copper pipe is MUCH more expensive than plastic geo-tubing and susceptible to oxidation and mechanical failure (e.g. you can punch a hole in a copper pipe pretty easily.)2 - the refrigerant is likley NOT to be environmentally save (a closed-loop ground-source heat-pump system uses a 50/50 mix of food grade glycol and water - leaks are claimed not to have any environmental impact. The same cannot be said for most refrigerant gasses.3 - I would expect the cost of install for a DX system to be higher than the ground-source closed-loop (as refrigerant costs more than glycol) so you'd want to factor that into your total cost and ROI calculations4 - Residential installs can get a rebate in certain states as well (NY / California / not sure of the others). I think it maxes out at 2k or 3k. I'm not aware of a federal rebate for a non-commercial install (e.g. single-family home.)5 - Ignorance expressed here: not sure if you can tie in the residential hot-water to a DX system (just don't know if they come with such a system tie-in available.) On our ground-source system, we ordered it with a built-in heat exchanger that heats our domestic hot water whenever the system is running. (Cuts your water-heating expense by 50~75%)

I bought a house in Minnesota (cold winters, hot summers) that was a part of a pilot program in the 80s by Northern States Power (now Xcel Energy), whereby the installation cost was subsidized by NSP for this home and a handful of others.

Upon learning about this from the previous owners, I was naturally concerned about the system's efficacy at heating and moreover cooling the split-level home as compared to traditional gas furnace and air conditioning. It wound up performing identically on both counts, providing as much heated or frosty air as desired seasonally, all for only the price of operating the heat pump; I believe the annual electric cost was roughly $80/year.

To top things off the house was furnished with a traditional gas furnace as a safety backup.

They are also quite common in Finland. Usually, a network of pipes is laid about 2 meters below ground level in the garden as the thermal reservoir (in less extreme climates, one meter deep may be enough). They have higher capital cost than the air-to-air heat pumps, but generate less noise and continue to operate even in very cold weather - unlike most air-to-air units, which get into trouble below -20C.

Recently we installed a new furnace (Ontario, Canada). My wife and I had it priced out.

Turns out that although there were several grants we could receive, totalling $7000 approximately, it was still not worth it.

By the time all was said and done, it would have cost $30k to install. They would have torn up our lawn, which would have necessitated new landscaping. They also couldn't guarantee that they wouldn't crush our water and sewage lines with the drilling trucks.

All in all, it wasn't 50% more expensive. After rebates, it would have been about 4 or 5 times what a 96% efficiency natural gas furnace cost us.

As noted in the articles, very few Ph and ground conditions can corrode copper, hence I object to the absolute ban of copper in the previous reply.

And yes copper is more expensive. But most plastics (PVC) cannot be used with refrigerants, so given a choice of metal pipes, copper makes sense in certain soil conditions.

With certain precautions, copper is the way to go in DX systems. I do agree with most of the above replies that closed loop is good too. I think that you have to weigh the intended use against the pros and cons, then select the best system for that application.

Side note to the OP, the phrase "geothermal" to most homeowners does mean ground-source heat pump technology, not the stuff they use in Greenland.

I have a modest 2000sqft home in northeastern PA (Poconos area, I'm 8 miles south of Camelback ski resort). I had two contractors out to quote ground-source DX (direct exchange) systems, and both quotes were in the mid-$20k range. Too rich for my blood.

I went with a Hallowell cold-weather heat pump [gotohallowell.com] for pleasantly less than half that. The Hallowell is mostly sold in Canada and upper New England, but it's been slowly working its way south. When I called them to ask about my application, the guy laughed and said "Man, you're in the tropics!"

It's only been running for a few weeks now, but I've been very impressed so far. It hit -3F two nights ago and the heat pump still ran entirely off the first compressors in stage 1 (stage 2 was still not needed). The air coming out of the vents was warm to the touch. In fact, the system has yet to resort to resistance heat down to -3F exterior temperatures. We keep our house set to 66F. I've been able to kick the heating oil furnace and storage tank to the curb. No more timing oil pre-buys against market prices, no more noisy power venters, no more oil storage tank taking up basement space, no more yearly burner tuneups and vent pipe cleanouts. I even get nice 18 SEER air conditioning to replace my builder-grade central air conditioning unit.

The entire system is on a dedicated subpanel, and I've put a subpanel meter on it to measure total kWh usage. This will allow me to directly measure operational cost each month.

Another factor that steered me away from ground-source is balancing the break-even time versus the system lifetime. If it takes me 20 years to break even on the ground-source and the system needs replaced not too long after, I haven't really gained anything. If the Hallowell takes me 7 years to break even and the system lasts 2-3 times longer than that, I've saved quite a bit of money. Break-even isn't everything; it has to be balanced against the expected lifetime of the system. Plus, I'd have to factor in the cost of repairing the yard after the loops were dug and installed. They claim that just a 3' circle of ground is disturbed to drill the loops, but one of the guys eventually admitted the machines rip up the yard pretty bad as they drive around the hole to drill the loops at different angles.

I found the guys at Hallowell to be very helpful to talk to. I don't work for them and I have nothing to gain. I simply speak as a satisfied customer. For new construction, rolling a ground-source system into the mortgage would be the way to go. For my existing construction with an established yard, simply setting the Hallowell on an outdoor pad was an excellent path forward for me.

I to live in Florida and have a ground water heat exchange system produced by ColdFlow. http://www.coldflow.com/My system is old enough I don't need to used an enclosed loop. Nice thing about that is every time the unit is running my yard is getting watered too. These systems are very efficient and with being in a cinder block house my electric bill runs about $100 a month.

We've been getting virtually free heating and cooling on our 64,000 cubic foot storage building for 20 years. We simply ran a 30 foot extension from the drainage tile in the neighboring field and put a fan on the end of it. Constant 60f air. Paying electricity for a medium sized fan beats the hell out of $3,000+ heating bills in February when it gets and stays below zero or August when it gets above 100f.

If a farmer could hack this together from spare parts 20 years ago, I can only hope that the technology has gotten much better since then.

I recall reading about someone in Hawaii doing something like this in order to both generate electricity and clean water by essentially using the deep ocean as the heat sink then the temperature differential to generate electricity

Ah yes, OTEC [wikipedia.org]. Has a somewhat high cost per kWh, but a neat technology in any case. You could even make a GTEC (same thing but with Ground instead of Ocean) power plant using a sufficiently large closed loop in soil, or a sufficiently large aquifer.

I did a little more research on this today. I lost my old bookmarks (switching computers too much, and reinstalling for fun), so I don't have the good sites. I did find a couple pages on Wikipedia though. Search "Ground-coupled heat exchanger" and "Geothermal heat pump".

I was talking to a friend in Alaska about this. A long time ago, I had read about setting up for the nuclear tests at Amchitka, Alaska. If I remember the details right, when they dug down to make the cavern, at about 100 feet, they were working in total darkness and effectively deaf due to the digging machine noises. The temperature was over 100 degrees due to geothermal activity. That's a long way from Anchorage though, even though both are geologically unstable (expect your pipes to break in the next earthquake). He took the opportunity to tell me about an earthquake in the 1964 that destroyed over 100 buildings in Anchorage. He noted one part of town that I drove through, that was a small valley, was flat land previous to 1964.:)

I was trying to find how deep they'd have to go in the Anchorage area to find warm ground. I found the building codes dictate all underground water pipes must be 10 feet deep. My friend confirmed that, but said even at 10 feet, they have water pipe freezes and bursts in the winter.

The purpose of that mental exercise was to find a way to warm a friend's cabin, in the middle of nowhere. The air temperature recently was 35F below zero, and that didn't account for the wind chill. Brrr.:)

I found this page [ornl.gov] which they tested such a system, where the air temperature would reach 10F. They buried their pipes 4 feet deep, but ran electric heat for 4 months of the year. They should have gone deeper.:)

I still haven't found a good answer for "how deep", but obviously 10 feet isn't enough in Anchorage. It probably requires a prolonged test with thermometers at different depths, to test the local conditions. I know soil composition makes a big difference too.

Here in Florida, if you go too deep, you find ground water pretty easily. Water wells can be as shallow as just a few feet here. When I was a kid, we had a water well, that was dug into a cavern at just about 30 feet.

I can't help but wonder about what would happen if a sufficient number of people in an area used heat pumps, long term.

This is one of the questions I address in my book, Sustainable Energy - without the hot air [withouthotair.com] (available from amazon, and for free (pdf) on the web). The chapter on "Smart Heating" highlights heat pumps. They are definitely going to be one of the pillars of the post-fossil-fuel future. With a typical suburban population density, there is indeed not enough ground area for everyone to get all their heating out of the ground, if they are not careful to put heat back at other times of year. If people suck too much heat, without putting it back, then the ground will gradually become frozen. There is a similar potential problem with ground source air-conditioning, where people use the heat pump the other way round a lot, dumping heat in the ground (or sucking cold, if you like). Eventually the ground warms up, and the A/C doesn't work so well. This has happened in central London. There are two fixes: (1) ensure that annual heat sucking matches annual heat dumping (by matching winter heating to summer A/C, and perhaps even adding solar hot water panels to the roof, to get extra heat to dump during the summer); or (2) use a heat pump but with a different heat source, for example the air. As already noted, air-source heat pumps are not great if you have -40 degree winters. But in many countries with mild winters (eg Britain) I think air-source heat pumps are the best choice for green heating. Sustainable Energy - without the hot air [withouthotair.com] also has an appendix on heat pumps in which the relevant equations are worked out from first principles.
David MacKay
Cambridge

Greenpeace is one of the biggest impediments to building new Nuclear plants in California where they are needed. Coal plants put more nuclear material into the air every year than all the nuclear tests and accidents EVER combined. I know a desk-rider and a former smokestack-climber in the pollution regulation industry and they both let me know in no uncertain terms that you can find people polluting over the EPA standards (whether those standards are even acceptable is a matter for debate) as fast as you can secure funding to send people up smokestacks. No joke. Meanwhile if we used breeder reactors (but try building a tried and true reactor, let alone something new) we could reduce our nuclear fuel consumption by a couple of orders of magnitude. Even a cofounder of Greenpeace has come out in favor of nuclear power, as he's realizing that moving to superior technology is more feasible than changing the consumption habits of the entire world. Unfortunately it is now far too late... Obama, meanwhile, is a Coal supporter. FWIW.